JP3627334B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to a drivability improvement technique by appropriate air-fuel ratio control such as a lean combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a so-called lean burn engine (hereinafter referred to as a lean burn engine) that burns at an air / fuel ratio leaner than a stoichiometric air / fuel ratio is known as an engine mounted on a vehicle.
In such a lean burn engine, the applicant sets a comprehensive lean region based on the fuel injection amount Tp equivalent to the mass air amount sucked into the engine as the engine load, the rotational speed Ne, the water temperature Tw, and the throttle valve opening TVO. Then, it has been proposed to determine the lean region based on these Tp, Ne, Tw, and TVO.
[0003]
That is, when all of FIGS. 5A to 5C are satisfied, it is determined that the region is a lean region.
If the lean region is determined, the target air-fuel ratio is determined from Tp and Ne from the map shown in FIG. 5 (A), and as shown in FIG. As the load (Tp) increases, the target air-fuel ratio is made rich so as to reduce torque shock when switching between lean operation and stoichiometric operation.
[0004]
[Problems to be solved by the invention]
However, such lean burn engine air-fuel ratio control technology has a problem that good drivability can be obtained at low altitudes, but good drivability cannot be obtained because the air density is low at high altitudes. There was room for improvement.
That is, in the case of a lowland, in the lean map as shown in FIG. 5A, the air-fuel ratio gradually changes from 24 → 23 → 22 → 21 as the fuel injection amount Tp or the rotational speed Ne increases. Torque shock is small.
[0005]
On the other hand, since the mass air amount does not increase even when the throttle valve opening is large at high altitudes, the throttle valve opening differs by a as shown in FIG. 6A, and therefore Tp corresponding to the mass air amount does not increase. Therefore, the lean region is determined from the map of FIG. 5A, but the determination in the map of FIG. 5C is out of the lean region.
[0006]
For this reason, a large throttle valve opening is triggered, for example, the air-fuel ratio is switched from 24 to 15, and a large torque shock is generated.
That is, on the map of the throttle valve opening TVO and the air-fuel ratio correction coefficient DML for obtaining the target air-fuel ratio shown in FIG. 6B, the DML change indicated by the alternate long and short dash line is shown. Since the lean / stoichiometric change occurs due to the degree of TVO, the step of the target air-fuel ratio at the time of this change becomes large as b ′ (b in the lowland) shown in FIG. 5B, and the torque shock becomes large.
[0007]
Although the above problem can be solved by providing an atmospheric pressure sensor and making a high altitude judgment, the atmospheric pressure sensor is expensive and the use of this is to be avoided.
There is also a technique for estimating the atmospheric pressure without providing an atmospheric pressure sensor. However, this estimation has a problem that the error is large and the estimation takes time, which is not preferable.
[0008]
Therefore, in view of the above-described conventional problems, the present invention aims to reduce torque shock at the time of switching by performing control to reduce the step of the target air-fuel ratio at the time of switching between lean and stoichiometric, for example. To do.
[0009]
[Means for Solving the Problems]
For this reason, as shown in FIG. 1, the invention according to claim 1 is equivalent to the throttle valve opening of the throttle valve interposed in the intake passage of the internal combustion engine , the engine rotational speed, and the mass air amount sucked into the engine. An engine operating condition detecting means for detecting an engine operating condition including a basic fuel supply amount, and a region where combustion is performed at an air-fuel ratio of a first concentration based on the engine operating condition detected by the engine operating condition detecting means At least for each of the combustion regions determined by the combustion region determining means, the combustion region determining means for determining whether the region is burned at an air-fuel ratio of a second concentration that is higher than the air-fuel ratio region of the first concentration; and air-fuel ratio correction coefficient calculating means for calculating the air-fuel ratio the engine speed correction coefficient and the basic fuel supply amount for obtaining a target air-fuel ratio which is determined based on the mass air quantity sucked into the engine, search Air-fuel ratio correction coefficient lower-limit value calculation means, air-fuel ratio correction coefficient limiting means for limiting the air-fuel ratio correction coefficient in the air-fuel ratio correction coefficient lower-limit value for calculating the air-fuel ratio correction coefficient lower-limit value corresponding to the throttle valve opening which is A fuel supply amount calculating means for calculating a fuel supply amount so as to obtain a target air-fuel ratio obtained by correction with an air-fuel ratio correction coefficient limited by the limiting means, and a fuel calculated by the fuel supply amount calculating means And a control means for controlling the fuel supply means so as to obtain a supply amount.
[0010]
According to a second aspect of the present invention, the region burned at the first concentration air-fuel ratio is a lean combustion region that is leaner than the stoichiometric air-fuel ratio, and the region burned at the second concentration air-fuel ratio is the stoichiometric air-fuel ratio. A stoichiometric combustion region or a rich combustion region richer than the stoichiometric air-fuel ratio was set.
[0011]
The invention according to claim 3 is provided with an engine temperature detecting means for detecting the engine temperature as the engine operating condition detecting means.
In the invention according to claim 4 , the lower limit value of the air-fuel ratio correction coefficient is set to a value that overcomes the calculated value of the air-fuel ratio correction coefficient in the vicinity of the fully opened throttle valve opening.
[0012]
The invention according to claim 5, wherein the air-fuel ratio correction coefficient lower-limit value, so as to gradually vary from a region to be burned in the air-fuel ratio of the first density to the area to be burned at an air-fuel ratio of the second concentration did.
[0013]
【The invention's effect】
According to the first and fifth aspects of the invention described above, by calculating the air-fuel ratio correction coefficient lower limit value corresponding to the throttle valve opening, and limiting the air-fuel ratio correction coefficient to the air-fuel ratio correction coefficient lower limit value, for example, The air-fuel ratio correction coefficient gradually changes when switching between lean and stoichiometry, making it possible to keep the target air-fuel ratio step small and to reduce torque shock. Good operation in both low and high altitude areas Sex can be secured.
[0014]
According to the second aspect of the invention, in a lean combustion engine that burns at a leaner air / fuel ratio than the stoichiometric air / fuel ratio, good drivability can be ensured in both low and high altitude areas.
According to the invention of claim 3, the air-fuel ratio region can be set comprehensively based on the engine speed, the basic fuel supply amount corresponding to the mass air amount, and the engine temperature, and the lean region can be accurately determined from these factors. it can.
[0015]
According to the fourth aspect of the present invention, it is possible to make the most of the region where the air-fuel ratio is burned at the first concentration (lean region in the lean combustion engine).
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 2 is a system configuration diagram of a lean burn engine as one embodiment of the internal combustion engine of the present invention. Air measured by an air flow meter 2 is sucked into the engine 1, and as such air and fuel supply means An air-fuel mixture having a predetermined air-fuel ratio is formed by the fuel injected from the fuel injection valve 3.
[0017]
Exhaust gas from the engine 1 is purified by a catalyst device 5 provided in the middle of the exhaust passage 4 and discharged.
The amount of fuel injected by the fuel injection valve 3 is controlled according to the pulse width of the injection pulse signal output from the control unit 6.
The control unit 6 has an engine rotational speed from a rotation sensor 7 that extracts an intake air amount (mass air amount) signal Qa from the air flow meter 2 and a rotation signal from a crankshaft or camshaft as engine operating condition detection means. Signal Ne, an oxygen concentration signal from an oxygen sensor (air-fuel ratio detection means) 8 provided in the exhaust passage 4 upstream of the catalyst device 5 to detect the oxygen concentration in the exhaust, and a valve opening degree detection means for the throttle valve 9 The throttle valve opening signal TVO from the throttle sensor 10 and the water temperature signal Tw from the water temperature sensor 11 for detecting the engine coolant temperature as the engine temperature are input.
[0018]
The oxygen sensor 8 is, for example, an oxygen concentration cell that generates an electromotive force according to the ratio of the reference oxygen concentration to the oxygen concentration in the exhaust gas, and corresponds to a sudden change in the oxygen concentration at the boundary of the theoretical air-fuel ratio. Thus, the sensor can detect the stoichiometric air-fuel ratio by increasing the output on the rich side and decreasing the output on the lean side than the stoichiometric air-fuel ratio.
Here, the engine 1 of the present embodiment is a lean burn engine that performs combustion at a lean air-fuel ratio of about air-fuel ratio = 22, and operates with lean air-fuel ratio combustion and stoichiometric combustion operation near the stoichiometric air-fuel ratio. The operation with rich air-fuel ratio combustion that is deeper than the stoichiometric air-fuel ratio is switched according to the operating conditions (for example, the rotational speed Ne and the basic injection pulse width Tp).
[0019]
Therefore, the control unit 11 is equipped with a function for appropriately selecting lean control, stoichiometric control other than lean control, and rich control, and the air-fuel ratio correction coefficient DML for obtaining the target air-fuel ratio is as shown in the flowchart of FIG. The fuel injection control is executed as shown in the flowchart of FIG.
That is, in the embodiment of the present invention, based on the rotational speed Ne, the basic injection pulse width Tp, the throttle valve opening TVO, and the water temperature Tw, the lean region in which combustion is performed at the lean air-fuel ratio as the first concentration air-fuel ratio. Or a combustion region determination means for determining whether the combustion region is a stoichiometric region or a rich region to be burned at the stoichiometric air-fuel ratio or rich air-fuel ratio as the air-fuel ratio of the second concentration that is higher than the air-fuel ratio region of the first concentration And an air-fuel ratio correction coefficient DML for obtaining a target air-fuel ratio determined on the basis of at least the mass air amount sucked into the engine for each combustion region determined by the combustion region determining means, the rotational speed Ne and the basic An air-fuel ratio correction coefficient calculating means for calculating by the injection pulse width Tp, and an air-fuel ratio correction function corresponding to the throttle valve opening TVO detected by the throttle sensor. Air-fuel ratio correction coefficient lower limit value calculating means for calculating the lower limit value DLMN, air-fuel ratio correction coefficient limiting means for limiting the air-fuel ratio correction coefficient DML to the lower limit value DLMN, and air-fuel ratio correction coefficient DML limited by the limiting means The fuel supply amount calculating means for calculating the fuel injection amount Ti so as to obtain the target air-fuel ratio obtained by correcting the fuel injection amount, and the fuel injection valve 3 is controlled so as to be the fuel supply amount calculated by the fuel supply amount calculating means. The control unit 6 is configured by software, and the functions of these means are installed in the control unit 6 by software.
[0020]
Next, the calculation of the air-fuel ratio correction coefficient DML for obtaining the target air-fuel ratio will be described based on the flowchart of FIG. 3 described above.
That is, in the flowchart, in step 1 (S1 in the figure, the same applies hereinafter), the lean region condition is satisfied or the stoichiometric region and rich region conditions are satisfied based on the rotational speed Ne and the basic injection pulse width Tp. It is determined whether or not. In this case, the condition determination is performed with reference to the map of FIG.
[0021]
In step 2, based on the throttle valve opening TVO, it is determined whether the lean region condition is satisfied or whether the stoichiometric region or rich region condition is satisfied. In this case, the condition determination is performed with reference to the map of FIG.
In step 3, it is determined based on the engine coolant temperature Tw whether the lean region condition is satisfied or whether the stoichiometric region or rich region condition is satisfied. In this case, the condition determination is performed with reference to the map of FIG.
[0022]
If it is determined that the lean region condition is satisfied in all of steps 1 to 3, the process proceeds to step 4 and if any of steps 1 to 3 is determined that the stoichiometric region or rich region condition is satisfied. , Go to step 5.
In step 4, an air-fuel ratio correction coefficient DML for obtaining a target air-fuel ratio for performing the lean region operation is calculated based on the rotational speed Ne and the basic injection pulse width Tp.
[0023]
In this case, an air-fuel ratio correction coefficient DML (for example, an air-fuel ratio 22 equivalent value) for obtaining a target air-fuel ratio referred to from the map of FIG.
In step 5, an air-fuel ratio correction coefficient DML for obtaining a target air-fuel ratio when performing stoichiometric region and rich region operation is calculated from the rotational speed Ne and the basic injection pulse width Tp.
[0024]
In this case, an air-fuel ratio correction coefficient DML (for example, an air-fuel ratio 15 equivalent value) for obtaining a target air-fuel ratio referred to from the map of FIG.
In step 6, an air-fuel ratio correction coefficient lower limit (limiter value) DLMN corresponding to the throttle valve opening TVO detected by the throttle sensor 10 is calculated.
[0025]
This limiter value is assigned by the throttle valve opening TVO as shown by the solid line in the map of FIG. 6C, and is read from the actual throttle valve opening TVO.
In the next step 7 and step 8, the air-fuel ratio correction coefficient DML is limited to the limiter value DLMN.
[0026]
That is, in step 7, DML and DLMN are compared. If DML> DLMN, the DML at that time is set as the air-fuel ratio correction coefficient. If DML ≦ DLMN, the process proceeds to step 8 to proceed to air-fuel ratio correction. The coefficient DML is limited to the limiter value DLMN (DML = DLMN).
Next, the state of fuel injection control will be described based on the flowchart of FIG. 4 described above.
[0027]
That is, in the flowchart, in step 11, the target air-fuel ratio equivalent amount TFBYA is calculated based on the equation (1), and in step 12, the basic injection pulse width Tp is calculated based on the equation (2).
TFBYA = DML + KAS + KTW + KHOT- (1)
However, DML: air-fuel ratio correction coefficient KAS: post-startup increase correction coefficient KTW: water temperature increase correction coefficient KHOT: post-warming increase correction coefficient Tp = (Qa / Ne) × K− (2)
However, in constant step 13 for determining Qa: intake air amount Ne: engine rotational speed K: base air-fuel ratio, the fuel injection pulse width Ti given to the fuel injection valve is obtained by the equation (3), and this is output to the output register in step 14 Forward.
[0028]
Ti = Tp × TFBYA × α × 2 + Ts− (3)
However, Tp: basic injection pulse width TFBYA: target air-fuel ratio equivalent amount α: air-fuel ratio feedback correction coefficient Ts: invalid pulse width According to the control content of the present embodiment described above, the following effects are obtained.
[0029]
That is, as described in the section of the prior art, at high altitude, the throttle valve opening TVO and the air-fuel ratio correction coefficient DML for obtaining the target air-fuel ratio shown in FIG. Although the DML changes, actually, the throttle valve opening TVO large is triggered to switch between lean and stoichiometric, and the step of the target air-fuel ratio at the time of this switching is shown in FIG. 6B. The torque shock becomes large with increasing '.
[0030]
As described above, the air-fuel ratio correction coefficient lower limit value (limiter value) DLMN corresponding to the throttle valve opening is calculated, and the air-fuel ratio correction coefficient DML is limited to the limiter value DLMN. The fuel ratio correction coefficient DML gradually changes along the limiter value DLMN shown by the solid line in FIG. 6C. As a result, the step of the target air-fuel ratio equivalent amount TFBYA can be suppressed to be small, and torque shock can be reduced. Can do.
[0031]
As a result, good drivability can be ensured in both the lowland and highland.
As a condition for determining the lean region operation, the lean region determination can be performed more comprehensively by adding the coolant temperature Tw as the engine temperature in addition to the engine rotation speed Ne and the basic injection pulse width Tp.
Also, the lower limit value of the air-fuel ratio correction coefficient is set to a value that exceeds the value of the air-fuel ratio correction coefficient DML calculated near the fully open throttle valve opening (point A), as shown in FIG. Preferably, this makes it possible to make the most of the lean region.
[0032]
In the above embodiment, an example in which the present invention is applied to a lean burn engine that burns at a leaner air / fuel ratio than the stoichiometric air / fuel ratio has been described. However, the present invention also applies to a normal engine that burns at a stoichiometric air / fuel ratio. The present invention can be applied.
In this case, as shown in FIG. 7, the air-fuel ratio correction coefficient that changes rapidly when switching from stoichiometric to rich as shown by the dotted line is limited by the limit of the air-fuel ratio correction coefficient by the limiter value as shown by the solid line in FIG. What is necessary is just to set so that it may change gradually.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of the present invention. FIG. 2 is a system diagram of an embodiment of the present invention. FIG. 3 is a flowchart showing a calculation routine of an air-fuel ratio correction coefficient DML. Flowchart [FIG. 5] Map explaining the lean region determination condition [FIG. 6] Characteristic diagram explaining the problems of the prior art and the operation of the present invention [FIG. 7] Characteristic diagram explaining another embodiment [Explanation of symbols]
1 Engine 2 Air Flow Meter 3 Fuel Injection Valve 6 Control Unit 7 Rotation Sensor 10 Throttle Sensor 11 Water Temperature Sensor

Claims (5)

Engine operating condition detecting means for detecting an engine operating condition including a throttle valve opening of a throttle valve interposed in an intake passage of the internal combustion engine , an engine speed, and a basic fuel supply amount equivalent to a mass air amount sucked into the engine; ,
Based on the engine operating condition detected by the engine operating condition detecting means, the air-fuel ratio of the second concentration is a region where combustion is performed at the air-fuel ratio of the first concentration or is higher than the air-fuel region of the first concentration. Combustion region determination means for determining whether the region is a region to be burned in,
For each combustion region determined by the combustion region determining means, an air-fuel ratio correction coefficient for obtaining a target air-fuel ratio determined based on at least the mass air amount sucked into the engine is used as the engine rotational speed and the basic fuel supply. An air-fuel ratio correction coefficient calculating means for calculating according to the amount ;
Air-fuel ratio correction coefficient lower limit value calculating means for calculating an air-fuel ratio correction coefficient lower limit value corresponding to the detected throttle valve opening;
Air-fuel ratio correction coefficient limiting means for limiting the air-fuel ratio correction coefficient to the air-fuel ratio correction coefficient lower limit value;
Fuel supply amount calculation means for calculating a fuel supply amount so as to obtain a target air-fuel ratio obtained by correcting with the air-fuel ratio correction coefficient restricted by the restriction means;
Control means for controlling the fuel supply means so as to be the fuel supply amount calculated by the fuel supply amount calculation means;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: The region burned at the first concentration air-fuel ratio is a lean combustion region leaner than the stoichiometric air-fuel ratio, and the region burned at the second concentration air-fuel ratio is the stoichiometric combustion region or stoichiometric air-fuel ratio of the stoichiometric air-fuel ratio. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the rich combustion region is richer. 3. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein an engine temperature detecting means for detecting an engine temperature is provided as the engine operating condition detecting means. The air-fuel ratio correction coefficient lower limit value, to any one of claims 1-3, characterized in that it is set to a value overcoming the value of the computed air-fuel ratio correction coefficient near fully open throttle valve opening An air-fuel ratio control apparatus for an internal combustion engine as described. Claims, characterized in that the air-fuel ratio correction coefficient lower-limit value, and from the area to be burned in the air-fuel ratio of the first density is gradually varied to a region to be burned in the air-fuel ratio of the second concentration The air-fuel ratio control apparatus for an internal combustion engine according to any one of 1 to 4 .

Images